Open-loop vertical drywell gradient correction system and method

ABSTRACT

A system and method are disclosed for controlling a drywell including a receiver having upper and lower ends with the lower end being more insulated than the upper end having a temperature sensor in thermal contact therewith. Upper and lower heating elements are in thermal contact with the upper and lower ends, respectively. A controller includes an integrated circuit having a temperature sensor. A reading from the integrated circuit is used to control power to the upper heating element and reduce a temperature gradient between the upper and lower ends of the receiver.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.13/049,716, filed Mar. 16, 2011, now U.S. Pat. No. 8,366,315, which is adivisional of U.S. patent application Ser. No. 11/940,244, filed Nov.14, 2007, now U.S. Pat. No. 7,909,504, the disclosures of which areincorporated by reference herein in their entirety.

TECHNICAL FIELD

This invention relates to systems and methods for controlling drywelltemperature.

BACKGROUND

It is typical for thermometers and thermal switches to be calibratedusing a drywell. Drywells may include a receiver in which a thermometeror thermal switch is inserted. A heating element and temperature sensorare in thermal contact with the receiver such that the temperaturewithin the receiver may be accurately set. The set temperature of thedrywell may then be compared to the readout temperature of thethermometer or the switching temperature of a thermal switch todetermine its accuracy. In some uses, a reference thermometer isinserted within the receiver along with the thermometer or switch beingcalibrated, and the readout of the reference thermometer is used forcalibration purposes.

It is important in some applications to provide a uniform temperaturegradient between the top and the bottom of the receiver such that thetemperature actually imposed on the probe is very close to the settemperature of the drywell or the readout temperature of the referencethermometer. In prior systems, two heating elements are used, one nearthe top of the receiver and another near the bottom. Two temperaturesensors, also located near the top and the bottom of the receiver,provide feedback. A controller receives signals from the temperaturesensors and drives the heaters such that the temperature sensorsindicate the same temperature.

The above-described approach is costly inasmuch as it requires twothermal sensors. The sensors used must be of extremely high quality andsensitivity inasmuch as they are used for calibration of thermometersand thermal switches that are themselves highly accurate. The sensorsmay need to be accurate over a broad range—from about 20 to over 600degrees Celsius. Due to the large temperature changes to which thesensors are subject and the need for accuracy, each of the sensors mayneed to be serviced or replaced during the life of the drywell. Theadditional sensor further increases expense by requiring additionalcircuitry and processing power to provide feedback control using theoutput of the sensor.

In view of the foregoing, it would be an advancement in the art toprovide a drywell using a single receiver-mounted thermal sensor withoutincreasing the cost or processing requirements of the drywell.

SUMMARY

In one aspect of the invention, a drywell includes a receiver into whichthe probe of a thermometer or thermal switch may be inserted. Thereceiver has upper and lower ends, with the upper end being exposed toambient air and the lower end being substantially more insulated thanthe upper end. An upper heating element is in thermal contact with theupper end and a lower heating element is in thermal contact with thelower end. A temperature sensor is also in thermal contact with thelower end. The only temperature sensors providing an output regardingthe temperature of the receiver are positioned within the insulatedlower end. In an alternative embodiment, the only temperature sensor islocated proximate the upper end.

A controller is coupled to the heating elements and the temperaturesensor to control the temperature of the receiver. The controller mayinclude a printed circuit board having an ambient temperature sensormounted thereon. The ambient sensor may be embedded within an integratedcircuit mounted to the printed circuit board. In one embodiment, theintegrated circuit is a dual mode circuit having operational and sensingmodes. The controller may switch the integrated circuit into the sensingmode in order to measure the ambient temperature.

The controller is programmed to monitor the receiver temperature,compare the receiver temperature to a set temperature, and to calculatea lower heater power value effective to drive the receiver temperaturetoward the set temperate. The controller also calculates an upper heaterpower value according to the ambient temperature reading and at leastone of the set temperature and the receiver temperature. The upperheater value is effective to drive the temperature of the upper end ofthe receiver toward the set temperature and compensate for heat loss tothe ambient from the upper end. The controller then supplies the upperheater value and the lower heater value to the upper and lower heaters,respectively.

DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisinvention will become more readily appreciated as the same become betterunderstood by reference to the following detailed description, whentaken in conjunction with the accompanying drawings, wherein:

FIG. 1 is an isometric view of a drywell in accordance with anembodiment of the present invention;

FIG. 2 is a side cross sectional view of a drywell in accordance with anembodiment of the present invention;

FIG. 3 is a schematic block diagram of a drywell in accordance with anembodiment of the present invention;

FIG. 4 is a process flow diagram of an open loop vertical gradientcorrection method in accordance with an embodiment of the presentinvention; and

FIG. 5 is a process flow diagram of an alternative embodiment of an openloop vertical gradient correction method in accordance with anembodiment of the present invention.

DETAILED DESCRIPTION

Referring to FIG. 1, a drywell 10 may include a housing 12. A vent plate14 may be secured near the top of the housing 12 and permit air to flowout of the drywell 10. The vent plate 14 defines an aperture 16positioned over a receiver 18. The receiver 18 includes one or moreapertures 20 sized to receive the probe 22 of a thermometer, thermalswitch, or the like. In use, the temperature of the receiver 18 iselevated to a specified temperature in order to test the thermalresponse characteristics and accuracy of the device being tested. Aheating element in thermal contact with the receiver 18 may be used tocontrol the temperature of the receiver 18.

The drywell 10 may include a control module 24 secured thereto.Alternatively, the control module 24 is remote from the drywell 10 andcoupled to the drywell 10 by wires or other communication means. Thecontrol module 24 may include an interface 26 for interacting with thedrywell 10. The interface 26 may include a display 28, input buttons 30,and ports 32 for coupling thermometers, thermal switches, and the liketo the control module 24 for testing.

Referring to FIG. 2, the drywell 10 may include a circuit board 34mounted within the control module 24. The circuit board 34 may include aprocessor 36 for executing executable data and processing operationaldata. In some embodiments, other integrated circuits 38 mount to thecircuit board 34 and are in data communication with the processor 36. Inthe illustrated embodiment, one of the integrated circuits 38 is a dualmode analog-to-digital (A/D) converter, having operational andtemperature sensing modes.

The circuit board 34 may be exposed to ambient air flow 40, whetheractive or passive. For example, a fan may supply air to the circuitboard 34. Alternatively, the control module 24 may be supplied withvents permitting convective air flow therethrough. The circuit board 34may be separated from the receiver 18 by a wall 42. The wall 42 may beformed of metal, plastic, or other material. The wall 42 may includeinsulation thermally isolating the circuit board 34 from the receiver18.

The receiver 18 may include insulation 44 surrounding a lower end 46thereof. The insulation 44 may extend up to the upper end 48, butleaving the upper end 48 exposed in order to permit insertion of theprobe 22. Accordingly, the upper end 48 is subject to heat loss toambient air flow 50 to a much greater extent than the lower end 46.

A shield 52 may extend between the lower end 46 and the upper end 48 ofthe receiver 18. A fan 54 positioned below the receiver 18 may directairflow 56 between the insulation 44 and the shield 52. The fan 54 mayalso induce airflow 58 between the shield 52 and the housing 12.

As is apparent from FIG. 2, the circuit board 34 is thermally isolatedfrom the receiver 18 by means of the active cooling induced by the fan54, the shield 52, and the wall 42. Thermal isolation may advantageouslyreduce heat related variation in the functioning of the circuit boardand prevent damage.

A lower heating element 60 is secured in thermal contact with thereceiver 18 proximate the lower end 46. A temperature sensor 62, such asa thermocouple or like sensor, may also be positioned in thermal contactwith the receiver 18 proximate the lower end 46. An upper heatingelement 64 may be secured in thermal contact with the receiver 18proximate the upper end 48.

The upper and lower heating elements 60, 64 may be controlled by thecircuit board 34. In some embodiments, intervening current handlingcircuits may be positioned electrically between the heating elements 60,64 and the circuit board 34 to supply actual current to the heatingelements 60, 64 subject to control signals from the circuit board 34.

Referring to FIG. 3, the control module 24 may include a feedbackcontrol module 66 in electrical communication with the temperaturesensor 62 and the lower heating element 60. The feedback control module66 may compare a reading from the temperature sensor 62 to a settemperature. The feedback control module 66 then determines an amount ofpower to supply to the lower heating element 60 in order to reach theset temperature.

The feedback control module 66 may communicate with a gradientcorrection module 68. The gradient correction module 68 determines froma measurement of ambient temperature a correction factor compensatingfor heat loss to the ambient. In the illustrated embodiment, thegradient control module 68 receives an input from the feedback controlmodule 66, such as a signal corresponding to one or more of the currentamount of power being supplied to the lower heating element 60, thecurrent set temperature, the current output of the temperature sensor,or some value derived from all or some of these factors. The feedbackcontrol circuit also receives a temperature measurement from theintegrated circuit 38 mounted to the circuit board 34. The gradientcorrection module 68 then calculates one or more correction factorsbased on the measurement from the integrated circuit 38 and the valuesreceived from the feedback control module 66.

In one embodiment, the gradient correction module 68 receives a valuecorresponding to the amount of power being supplied to the lower heatingelement 60 and either the set temperature or measured temperature. Thegradient correction module 68 may then add a correction factor to theamount of power being supplied to the lower heating element 60, multiplyit by a correction factor, or both to determine a corrected power value.The gradient correction module 68 then drives the upper heating element64 according to the corrected power value. In some embodiments, thetemperature measurement of the integrated circuit 38 is supplied to thefeedback control module 66 in order to determine the amount of power tosupply to the lower heating element 60.

The feedback control module 66 and gradient correction module 68 may beimplemented as digital or analog circuits or as code executed by aprocessor or by some other means. The components performing the functioncorresponding to these modules 66, 68 may be in the same or differentphysical or logical locations. The functions attributed the modules 66,68 may be performed by the same component simultaneously ornon-simultaneously.

Referring to FIG. 4, a method 70 for controlling a drywell 10 mayinclude measuring the temperature of the receiver 18 proximate the lowerend 46 at block 72. Block 72 may include measuring the temperature of abody in thermal contact with the receiver 18. At block 74, a settemperature and the temperature measured at block 72 are compared. Atblock 76 the amount of power to be supplied to the lower heater 60 iscalculated based on the comparison at block 74. The power may becalculated as a voltage, current, or a unit of energy such as watts. Theamount of power to be supplied may correspond to the difference betweenthe measured and set temperatures according to known principles ofcontrol dynamics.

At block 78, the ambient temperature is measured. At block 80, one ormore correction factors are calculated. The correction factors may beused to calculate the power to the upper heater 64. For example, thecorrection factors may be multiplied by, or added to, or otherwisecombined with the power value calculated at block 76 for the lowerheater 60 such that the temperature gradient between the upper end 48and lower end 46 due to heat loss to the ambient will be reduced.

At block 82, the amount of power to be supplied to the upper heater 64is calculated. Block 82 may include combining the correction factor withthe value calculated at block 76 or by calculating a power valueaccording to the temperature measured at block 78 and one or both of theset temperature and the temperature measured by the temperature sensor62. The upper power value is preferably effective to substantiallyreduce the temperature gradient between the upper and lower ends 48, 46caused by heat loss to the ambient.

At block 84, the power value calculated at block 76 is supplied to thelower heater 60 and at block 86, the power value calculated at block 82is supplied to the upper heater 64. The method 70 may repeatperiodically or substantially continuously.

Referring to FIG. 5, in an alternative embodiment, the step of measuringambient temperature at block 78 may be replaced by the illustratedsteps. At block 88, the temperature of the controller is measured. Thismay include measuring the temperature of the circuit board 34 comprisingthe control module 24, for example, the integrated circuit 38 mayinclude a temperature sensor providing a reading of the temperature ofthe integrated circuit 38. Inasmuch as the circuit board 34 is exposedto the ambient airflow 40, the temperature of the circuit board 34 andthe integrated circuit 38 at steady state will be reflective of theambient temperature. In some embodiments, block 88 may include switchingthe integrated circuit 38 from an operational mode, such as functioningas an A/D converter, to a sensing mode at block 90. The output of theintegrated circuit 38 is read at block 92. Block 88 may also includeswitching the integrated circuit back to the operational mode at block94.

Although the present invention has been described with reference to thedisclosed embodiments, persons skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention. Such modifications are well within the skillof those ordinarily skilled in the art. Accordingly, the invention isnot limited except as by the appended claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A method for controllinga drywell comprising: measuring a receiver temperature proximate a lowerend of a receiver having an upper end opposite the lower end, whereinthe lower end is substantially more insulated than the upper end,wherein the receiver has an upper heating element in thermal contactwith the receiver proximate the upper end and a lower heating element inthermal contact with the receiver proximate the lower end, and wherein athermal sensor is in thermal contact with the receiver proximate theupper end; comparing the receiver temperature to a set temperature;based on the comparison, calculating a lower end power value that issubstantially effective to drive the receiver temperature to the settemperature; measuring an ambient temperature; determining a heat lossgradient based on the receiver temperature and the ambient temperature;powering the lower heating element according to the lower end powervalue; and powering the upper heating element according to an upper endpower value determined as a function of the heat loss gradient and thelower end power value.
 2. The method of claim 1, wherein the upper endpower value is determined so as to reduce a temperature differencebetween the lower end and upper end of the receiver.
 3. The method ofclaim 1, wherein the upper end power value is determined by multiplyingthe lower end power value by the heat loss gradient.
 4. The method ofclaim 1, wherein the upper end power value is determined by adding theheat loss gradient to the lower end power value.
 5. The method of claim1, wherein measuring the ambient temperature comprises measuring acircuit board temperature of a circuit board thermally isolated from thereceiver, and wherein the circuit board controls power to the upper andlower heating elements.
 6. The method of claim 5, wherein the circuitboard comprises an integrated circuit having an operational mode and asensing mode, and wherein measuring the circuit board temperaturecomprises switching the integrated circuit into the sensing mode tomeasure the ambient temperature.
 7. The method of claim 5, furthercomprising directing ambient airflow over the circuit board and thereceiver.
 8. A method for controlling a drywell comprising: measuring areceiver temperature proximate a lower end of a receiver having an upperend opposite the lower end, wherein the lower end is substantially moreinsulated than the upper end, wherein the receiver has an upper heatingelement in thermal contact with the receiver proximate the upper end anda lower heating element in thermal contact with the receiver proximatethe lower end, and wherein a thermal sensor is in thermal contact withthe receiver proximate the upper end; comparing the receiver temperatureto a set temperature; based on the comparison, calculating a lower endpower value that is substantially effective to drive the receivertemperature to the set temperature; measuring an ambient temperature;determining a heat loss gradient based on the set temperature and theambient temperature; powering the lower heating element according to thelower end power value; and powering the upper heating element accordingto an upper end power value determined as a function of the heat lossgradient and the lower end power value.
 9. The method of claim 8,wherein the upper end power value is determined so as to reduce atemperature difference between the lower end and upper end of thereceiver.
 10. The method of claim 8, wherein the upper end power valueis determined by multiplying the lower end power value by the heat lossgradient.
 11. The method of claim 8, wherein the upper end power valueis determined by adding the heat loss gradient to the lower end powervalue.
 12. The method of claim 8, wherein measuring the ambienttemperature comprises measuring a circuit board temperature of a circuitboard thermally isolated from the receiver, and wherein the circuitboard controls power to the upper and lower heating elements.
 13. Themethod of claim 12, wherein the circuit board comprises an integratedcircuit having an operational mode and a sensing mode, and whereinmeasuring the circuit board temperature comprises switching theintegrated circuit into the sensing mode to measure the ambienttemperature.
 14. The method of claim 12, further comprising directingambient airflow over the circuit board and the receiver.
 15. A methodfor controlling a drywell comprising: measuring a receiver temperatureproximate a lower end of a receiver having an upper end opposite thelower end, wherein the lower end is substantially more insulated thanthe upper end, wherein the receiver has an upper heating element inthermal contact with the receiver proximate the upper end and a lowerheating element in thermal contact with the receiver proximate the lowerend, and wherein a thermal sensor is in thermal contact with thereceiver proximate the upper end; comparing the receiver temperature toa set temperature; based on the comparison, calculating a lower endpower value that is substantially effective to drive the receivertemperature to the set temperature; measuring an ambient temperature;determining a heat loss gradient based on the receiver temperature, theset temperature, and the ambient temperature; powering the lower heatingelements according to the lower end power value; and powering the upperheating element according to an upper end power value determined as afunction of the heat loss gradient and the lower end power value. 16.The method of claim 15, wherein the upper end power value is determinedso as to reduce a temperature difference between the lower end and upperend of the receiver.
 17. The method of claim 15, wherein the upper endpower value is determined by multiplying the lower end power value bythe heat loss gradient.
 18. The method of claim 15, wherein the upperend power value is determined by adding the heat loss gradient to thelower end power value.
 19. The method of claim 15, wherein measuring theambient temperature comprises measuring a circuit board temperature of acircuit board thermally isolated from the receiver, and wherein thecircuit board controls power to the upper and lower heating elements.20. The method of claim 19, wherein the circuit board comprises anintegrated circuit having an operational mode and a sensing mode, andwherein measuring the circuit board temperature comprises switching theintegrated circuit into the sensing mode to measure the ambienttemperature.
 21. The method of claim 19, further comprising directingambient airflow over the circuit board and the receiver.